Gallium nitride and its aluminum and indium compound semiconductor alloys have been a focus of intense research effort because of their importance in light-emitting, lasing, high-frequency, high mobility, and high-power devices. Due to the lack in availability and high prices of bulk GaN substrates, GaN is typically grown heteroepitaxially on foreign substrates, such as sapphire, SiC, and Si. When these devices are operated in high power conditions, their performance is often limited by the poor electrical and thermal conductivity of the substrates. A widely adopted solution to this problem is to remove or lift off the substrates and bond the thin epilayers on thermally conductive submount materials, such as metal. However, direct growth of GaN on metal substrates would allow more ideal device performance by providing improved heat dissipation and current spreading capability, and avoiding the need for the lift-off and bonding processes. The feasibility of GaN heteroepitaxy on metal has been demonstrated on single crystalline Cu, Mo, Fe, and W substrates. See S. Inoue et al., Appl. Phys. Lett. 88, 261910 (2006); K. Okamoto et al., J. of Cryst. Growth 311, 1311 (2009); K. Okamoto et al., Appl. Phys. Lett. 93, 251906 (2008); and G. Li et al., Appl. Phys. Lett. 89, 241905 (2006). The growth technique of these works was pulsed laser deposition at low growth temperatures ranging from 450 to 700° C. In addition, Zhu et al. recently demonstrated the epitaxial growth of GaN on lattice-matched metallic substrates. See Zhu et al., U.S. Pat. Appl. Pub. 2011/0117376. However, this technique required one-axis lattice matching of the c-plane of wurtzite GaN to the (110) crystalline plane of the tungsten substrate and is not generally feasible for other metallic substrates.
Therefore, a need remains for a facile method of Group III-nitride heteroepitaxy on metal substrates using metal-organic chemical vapor deposition (MOCVD), which is the most adopted growth technique for Group III nitride devices in industry and academia.